High thermoelectric performance and anisotropy studies of n-type Mg3Bi2-based single crystal

Layered high-performing Mg ₃Bi ₂ -based materials which made from nontoxic and earth-abundant elements have been considered as a promising thermoelectric candidate for low-grade energy recycling. High-quality compositionally controllable Mg ₃Bi ₂ -based single crystals are grown using modified Bridgman method. The anisotropy of in- and out of plane in high-quality Mg ₃Bi _1.49Sb _0.5Te _0.01 bulk single crystals are clearly characterized, record high ZT of ∼0.9 at 300 K as well as excellent ZT _avg of 1.26 in the temperature range of 300-523 K are achieved along ab-plane, both of which rank as top values among the reported literature. Owing to the higher mobility (266 vs 189 cm ²·V ⁻¹·s ⁻¹ ), the electrical conductivity along ab-plane is about 25% larger than that along c-axis at room temperature. Besides, Seebeck coefficient and lattice thermal conductivity are insensitive to the direction, resulting in anisotropy of thermoelectric performance but smaller than van der Waals layered materials. Compared with parent Mg ₃Bi _1.5Sb _0.5, both carrier concentration and mobility are significant improved with quantitative Te doping, leading to greatly enhanced power factor. With in-depth investigations of anisotropy, the results presented here will advance the fundamental understanding of Mg ₃Bi ₂ -based system and suggest new ideas on design of the state-of-art thermoelectric materials with high performance.